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ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net 2012, 9(3), 1357-1363
Simultaneous Determination of Cobalt (II) and Nickel
(II) By First Order Derivative Spectrophotometry in Micellar
Media
RAJNI ROHILLA and USHA GUPTA*
Department of Chemistry,
Punjabi University Patiala, Punjab, India.
Received 31 October 2011; Accepted 01 February 2012
Abstract: A first-derivative spectrophotometry method for the simultaneous
determination of Co (II) and Ni (II) with Alizarin Red S in presence of Triton
X-100 is described. Measurements were made at the zero-crossing
wavelengths at 549.0 nm for Co (II) and 546.0 nm for Ni (II). The linearity is
obtained in the range of 0.291- 4.676 μg/ml of Ni (II) and 0.293- 4.124 μg/ml
of Co (II) in the presence of each other by using first derivative
spectrophotometric method. The possible interfering effects of various ions
were studied. The validity of the method was examined by using synthetic
mixtures of Co (II) and Ni (II). The developed derivative procedure, using the
zero crossing technique, has been successfully applied for the simultaneous
analysis of Co (II) and Ni (II) in spiked water samples.
Keywords: Cobalt (II), Nickel (II), Alizarin Red S, Triton X-100 , derivative spectrophotometry.
Introduction:
Nickel and cobalt metals are significant for environmental surveillance, food control,
occupational medicine, toxicology and hygiene. Cobalt alloys are used in some industrial
products because of their sufficient hardness and resistance against oxidation at high
temperatures. Cobalt-60 is used as an efficient radioactive tracer and an anti-cancer
treatment agent in medicine. Vitamin B12 (cyanocobalamin) is important for biological
activities1. Even though cobalt is not considered to be as toxic as most of the heavy metals,
it is an equally harmful element. Toxicological effects of large amounts of cobalt include
vasodilatations, flushing, and cardiomyopathy in humans and animals.
Nickel is the metal component of the enzyme urease and as such is considered to be
essential to plants and some domestic animals. Nickel can cause allergic reactions and that
certain nickel compounds may be carcinogenic 2.The determination of cobalt and nickel in
USHA GUPTA 1358
various samples in which it is found at low levels requires the use of sensitive and selective
procedures.
Among various methods that have been developed for the simultaneous determination
of nickel and cobalt are Atomic absorption spectrophotometry (AAS) using Flame atomic
absorption spectrophotometry (FAAS)3 or Electrothermal atomization Atomic absorption
spectrophotometry (ETAAS)4-6, high performance liquid chromatography7-10, chelation
ion chromatography11-12, electroanalytical techniques13-15,Neutron activation analysis
(NAA)6, X-ray fluorescence (XRF)17-18, and spectrophotometric methods19-22.UV-
Visspectrophotometric analytical procedures are most widely used for the simultaneous
determination of metals .The obvious reasons being experimental simplicity, rapidity and the
wide applicability of these procedures. In many cases traditional techniques are not suitable
for simultaneous determination because, the absorption spectra overlap and are not suitable
for simultaneous quantative analysis. Derivative spectrophotometry has been an extremely
useful technique for the simultaneous determination of binary mixtures.
Derivative spectrophotometry in the UV-V is region is a useful technique for
determining the concentration of a single component in binary and ternary mixtures of
compounds whose spectra shows considerable overlap. It is possible to measure the absolute
value of the derivative of the sum curve at an abscissa value (wavelength) corresponding to
a zero-crossing of one of the components in the mixture. This is termed as zero-crossing
measure and can be applied to the first derivatives. The zero-crossing derivative
spectrophotometry mode allows the resolution of binary mixtures of analytes by recording
their derivative spectra at wavelengths at which one of the components exhibits no signal.
Zero-crossing measurements for each component of the mixture are therefore the sole
function of the concentration of the others.
This paper reports a simple, sensitive and highly selective first order derivative
spectrophotometry method for simultaneous determination of nickel and cobalt. The method
is based on the formation of the complexes of Ni (II) and Co (II) with Alizarin Red S in
Triton X-100 micellar media.
Experimental:
Apparatus:
UV-visible absorbance spectra were recorded on a Shimadzu UV-1800 scanning
spectrophotometer. Digital century pH-meter CP 901 with a combined glass electrode was
used for pH measurements.
Reagents:
All the reagents used were of analytical reagent grade unless otherwise stated and double
distilled water was used throughout the experiment. A 0.1% (w/v) solution of Alizarin Red S
in doubly distilled water was prepared. Stock solution of Ni (II) and Co (II) (1×10-2
M) were
prepared. A buffer solution of pH 7.0 was prepared from ammonia and ammonium chloride
at appropriate concentration and 1% Triton X-100 solution was prepared in hot distilled
water.
General Procedure:
A 2.0 mL volume of buffer solution of pH 7.0, 1.0 mL of (0.1%) ARS solution, an
appropriate volume of Co (II) and Ni (II) and 2.0 mL of Triton X-100 were added to a 10
mL standard flask and final volume of the solution was adjusted with distilled water. The
Simultaneous determination of Cobalt (II) and Nickel (II) 1359
absorbance of the mixtures were measured in the wavelength range 480.0 – 640.0 nm
against reagent blank solutions in the first derivative mode.
Results and Discussions:
Absorption Spectra:
The normal absorption spectra of Co(II)-ARS complex and Ni(II)-ARS complex in the
presence of Triton X-100 showed the absorbance maxima at 549.0 nm and 546.0 nm,
respectively (Figure 1). Since the spectral bands of complexes overlap, the determination of
cobalt and nickel in their mixtures by zero-derivative is frequently impossible. By using
derivative spectrophotometry, we could analyse these samples simultaneously.
Figure 1. Absorption spectra of mixture of Co (II) and Ni (II) with 1.0 mL ARS (0.1%)
solution and 2.0 mL Triton X-100(1%) at pH 7.0.
Effect of pH:
Absorbance for both complexes was studied over a wide range of pH from 2.0 - 9.0. The
studies showed that the absorbance was maximum in the pH range 6.0 -7.0 for both
complexes (Figure 2). Hence, further studies were carried out at pH 7.0.
Nature of Surfactant:
The effect of nature and concentration of different surfactants such as Sodium lauryl
sulphate (SLS), Cetyltrimethylammonium bromide (CTAB), Cetylpyridinium bromide
(CPB), Triton X-100, Tween-80, and Tween-20 on the absorbance of Ni (II)-ARS and Co
(II) –ARS complexes was studied and it was observed that complex formation is faster,
stable and maximum in presence of Triton X-100, so it was selected as micellizing agent for
further studies. The effect of concentration of Triton X-100 on sensitivity of the method was
studied by varying its percent concentration from 0.5-3.0 % (w/v) and its volume from 0.5-
3.5 mL. The maximum absorbance was found with 2.0-2.5 mL of 1 % Triton X-100. Hence
2.0 mL of 1% Triton X-100 was used for further studies.
USHA GUPTA 1360
Figure 2. Effect of pH on the change in the absorbance of Co (II) and Ni (II)-ARS
complexes.
Figure 3. Effect of surfactants on complex formation of Co (II) and Ni (II).
Derivative Spectra:
First order derivative spectra of Co (II) and Ni (II) complexes were studied. Calibration
graphs for first derivative spectra were obtained by using the zero-cross over technique. Two
sets of mixtures were studied: one with increasing amounts of Co (II) from 0.293- 4.124
µg/mL at constant concentration of Ni (II) and a second with increasing amounts of Ni (II)
from 0.291- 4.676 µg/mL at constant concentration of Co (II). The height h2 and h1 in the
first derivative spectrum of mixture (See Figures 4 and 5) at wavelengths 546.0 nm and
Effect of different surfactants
Simultaneous determination of Cobalt (II) and Nickel (II) 1361
549.0 nm is proportional to the nickel and cobalt concentrations, respectively. The
calibration graph for Ni (II) and Co (II) was obtained by plotting absolute value of ∆h
against the concentration of Ni (II) and Co (II).
Figure 4. First order derivative spectra of solutions containing fixed concentration of Nickel
1.172 µg/ml and different concentration of Cobalt.
Figure 5. First order derivative spectra of solutions containing fixed concentration of Cobalt
0.883 µg/ml and different concentration of Nickel.
h1
h1
h2
wavelength, nm
USHA GUPTA 1362
Statistical Analysis of Results:
Various statistical parameters were calculated for Co (II) and Ni (II) with first order
derivatives. The calibration graphs obtained by recommended methods were linear over a
range of 0.293- 4.124 µg/mL for cobalt in the presence of 1.172 µg/mL of nickel and 0.291-
4.676 µg/mL for the nickel in the presence of 0.883 µg/mL cobalt (Table 1). The values of
correlation coefficients and intercepts on the axes indicate the good linearity of all the
calibration graphs and correspondence to Beer’s law for the first derivative measurements
Also it can be seen that the first derivative values of cobalt and nickel complexes at 549 and
546 nm, respectively, have a good precision due to lower values of RSD.
Table 1. Statistical analysis for the simultaneous determination of nickel and cobalt.
Metal Order of
derivative
λ(nm) Regression Equation r2 Linear range
(µg/m L)
R.S.D
Ni(II) Ist 546.0 Y=0.014x+0.001 0.999 0.291-4.676 0.66
Co(II) Ist
549.0 Y=0.016x+0.002 0.999 0.293-4.124 0.780
Interference Analysis
The effect of various diverse ions on the absorbance of a solution containing 0.5 μg/mL each
of nickel and cobalt was studied. An ion was considered to interfere when its presence
produced a variation in the absorbance of the sample greater than 5%. Among the anions
examined I-, Br
-, Cl
-, CO3
2-, SO3
2-, SO4
2-, NO
3-, IO
3-, NO2
- , SCN
- , acetate, thiosulphate did
not interfere at concentrations 1000 times higher than those of the analytes but
ethylenediamine tetraacetate and oxalate ions interfered strongly. Among the cations Hg2+
,
Cd2+
, Cu2+
, and Fe
2+ were masked with 1.0 mL of 5% sodium fluoride solution. Bi
2+and Pb
2+
were masked with 2.0 mL of 1 M sodium citrate solution.
Application of the Method
The proposed method has successfully been applied for Co (II) and Ni (II) determination.
Several spiked samples were prepared by adding aliquots of Nickel and Cobalt solutions to
river and tap water samples .The results are given in Table 2.
Table 2. Determination of nickel and cobalt in different real samples.
Concentration, µg/mL
Sample Spiked Found
Nickel Cobalt Nickel Cobalt
Tap water* 2.916 2.996 2.918 2.998
Tap water** 1.171 1.178 1.172 1.181
Ganga river Water 1.171 1.178 1.173 1.174
or (Ganga jal)
Tap water*-Punjabi University campus. Tap water**-Urban Estate, Patiala.
Simultaneous determination of Cobalt (II) and Nickel (II) 1363
Conclusion
The proposed method offers significant advantages over conventional methods because of
its speed and ease of operation. This method works without the need of preconcentration or
extraction steps. Thus, the inherent errors involved in these time-consuming steps using
toxic and carcinogenic organic solvents are avoided, and determination in aqueous phase
using micellar system makes the procedure eco-friendly. The proposed derivative
spectrophotometric method has comparable sensitivity with a low detection limit. Moreover,
low cost of the instrument, easy handeling, lack of requirement for consumable and almost
no maintenance have made spectrophotometry still a popular technique.
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